LANSING — As the number of abandoned bikes grows on college campuses, bike rental programs flourish.

In New York, abandoned bikes are recycled or trashed. In Denver, they are auctioned and the proceeds go to the city’s general fund. Elsewhere they are donated to charities. But in Michigan, some colleges are recycling them into bike rental programs.

The University of Michigan and Western Michigan University have programs stocked with brand new bikes. Some universities, such as Grand Valley State and Michigan State University, save money by reusing bikes left behind by students. Abandoned bikes are an excellent resource to get a bike rental program started, said Tim Potter, sustainable transportation manager at Michigan State.

“It’s a very cost-effective, environmentally-friendly way to start up a bike program and perhaps grow it into a full-on bike center,” Potter said. “People really start to get behind it when you can show some activity.”

MSU police impounded 1,548 bikes in 2015. This year, the number is already up to 1,509. Though many bikes are reclaimed by the owners, the ones left behind are sold. Potter, who manages the MSU Bikes Service Center, picks through them every year. The MSU bike rental program started in 2003 as a volunteer-run program. Its success enabled MSU to form the service center in 2006.

Without free abandoned bikes, the program may have never gotten off the ground, Potter said. Since 2003, abandoned bikes have been reclaimed, repaired and, until a few years ago, rented out by the university. Now that the program is popular enough, the rental fleet is stocked with brand new bikes, Potter said. However, abandoned bikes are still refurbished and sold at the service center.

Grand Valley has a similar rental program that still uses abandoned bikes. Campus police picked up 76 bikes by the end of the 2016 school year, 23 more than last year, according to Sgt. Jeff Stoll of the campus police.

“Our bike program facilitator has the option to check our inventory after the six-month hold period,” Stoll said. “The bikes he selects are used to increase the rental program and inventory.”

Grand Valley has a smaller program but only charges $5 per day or $25 per semester.

Central Michigan University Police counted 76 abandoned bikes over the summer, 19 more than last summer, said Service Officer Michael Anderson of the CMU Police. CMU does not have a rental program that repurposes abandoned bikes, so those bikes end up at the campus university store, where they are sold or auctioned off.

“Every now and then we do donate a bike or two to a charity that is in need of a bike for special occasions,” Anderson said. “Not very often though.”

Whether or not campuses have a bike program, abandoned bikes will always be around, Potter said. Problems like a flat tire can often lead to someone neglecting their bike.

“Some abandoned bikes, that’s their only problem,” Potter said. “They have a flat tire, they’re left on the racks over the winter and they get so rusty by spring that they’re not rideable anymore.”

Brand new bikes suffer the same fate.

“Now that we’ve been selling new bikes for a while, it amazes me to find bikes that I know we’ve sold and I know the price,” Potter said. “And now they’re starting to show up as abandoned bikes. It’s pretty sad.”